This patent application is co-pending with or related patent Application entitled xe2x80x9cQUIET AND EFFICIENT HIGH-PRESSURE FAN ASSEMBLYxe2x80x9d (Navy Case No. 82260), filed on the same date and owned by the same assignee as this patent application.
The invention relates generally to fan rotors, and more particularly to a fan rotor that is optimized for use in a high-pressure axial flow fan assembly.
U.S. Navy ships incorporating the Collective Protection System (CPS) in their ventilation system design use vane-axial (in-line duct) supply fans that are required to develop pressures that are substantially greater than those developed by conventional ventilation system fans. These CPS high-pressure ventilation supply fans are designed to overcome normal system pressure losses as well as pressure losses associated with a series of specialized air filters. In addition, the typical CPS supply fan must also be capable of maintaining a pressurized zone within the ship""s hull.
Current U.S. Navy CPS ventilation systems use conventional fan technology in-terms of rotor blade and stator vane configurations. That is, rotor blades are typically based on profiles of blended circular arcs that are not necessarily the most efficient from an aerodynamic perspective, and not the quietest from an aero-acoustic perspective. Aerodynamic inefficiencies and noise sources in the high-pressure fan assemblies include rotor blade vortex generation, flow separation from both rotor blades and stator vanes, and the interaction of the air as it transitions from rotor blades to stator vanes. The conventional solution for a low efficiency fan design involves the use of a higher horsepower fan motor to perform the aerodynamic work. The conventional solution used to keep the airborne noise levels within the required U.S. Navy specification for allowable space noise levels involves the use of a greater amount of acoustic attenuation material. Neither of these conditional solutions is desirable.
The afore-referenced co-pending patent application discloses a van-axial fan assembly that is addresses the issues of aerodynamic efficiency and noise. Briefly, this application discloses a fan assembly having a hub defining an axis of rotation with a plurality of rotor blades disposed circumferentially around and extending radially outward from the hub. Each rotor blade is constructed to define a straight-ruled leading edge that extends outward from the hub. There is unequal angular spacing between leading edges of adjacent ones of the rotor blades. Each rotor blade has a trailing edge that extends from the hub at a skew angle measured in a radial plane of the hub with respect to a first line extending radially outward from the axis of rotation. Each rotor blade has an axial chord length defined across a central portion thereof parallel to the hub""s axis of rotation. The plurality of rotor blades further defines a solidity of greater than 1. A plurality of stator vanes are disposed circumferentially around and extend radially from a frame. There are a lesser number of stator vanes than rotor blades. Each stator vane has a leading edge that extends from the frame at: i) an inclined angle measured in the radial plane with respect to a second line extending radially outward from the axis of rotation, and ii) a lean angle measured in an axial plane of the frame with respect to a third line extending radially outward from the axis of rotation. The frame with its stator vanes is positioned adjacent hub and rotor blades such that an axial gap is defined between the trailing edge of the rotor blades and the leading edge of the stator vanes. The axial gap increases with radial distance from the hub as defined by the skew angle and incline angle.
Issues left unresolved by this innovative fan assembly revolve around optimization of both mechanical construction techniques and safety performance criteria for the fan assembly""s rotor. A goal of such optimization is to minimize changes to the rotor""s aerodynamic and noise characteristics while achieving both a lightweight, cost-effective construction that performs within acceptable stress levels.
Accordingly, it is an object of the present inventions to provide a fan rotor for use in a high-pressure vane-axial fan assembly.
Another object of the present invention is to provide construction techniques for a high-pressure fan rotor that are cost-effective.
Still another object of the present invention is to provide construction techniques for producing a lightweight high-pressure fan rotor.
Yet another object of the present invention is to provide construction techniques for producing a fan rotor that achieves acceptable levels of stress performance.
A further object is to provide methods for optimizing an existing fan rotor design in terms of stress level performance while minimizing effects on the fan rotor""s previously-designed aerodynamic characteristics.
Other objects and advantages of the present invention will become more obvious hereinafter in the specification and drawings.
In accordance with the present invention, a one-piece fan rotor is optimized for construction and safety performance criteria. The rotor can be sand cast to meet cost restrictions. The rotor has a hub with a radial cross-section defined by an I-beam. Specifically, the I-beam shape is defined by an inner annular flange and an outer annular flange coupled to one another by an annular disk. A plurality of unequally-spaced rotor blades are disposed circumferentially around and extend radially outward from the outer annular flange of the hub. Each rotor blade has a root portion coupled to the hub with the root portion defined by a concave fillet circumventing the rotor blade. For balancing purposes, the hub incorporates at least one axially extending pad positioned out of the air flow about the rotor. In a cast rotor assembly, the pads are cast in place. In a machined rotor assembly, the pad is formed as part of an axially extending ring with an angular portion of the ring having an increased axial length relative to a remainder of the ring. Stress on the rotor is controlled by adjusting the radius of curvature of the concave fillet at the blade""s root, and by adjusting radial thickness of the hub""s outer annular flange.